The specific goal is to provide a better understanding of tryptophan and lysine catabolism and of regulatory interactions of their pathways that may be important in normal or pathological functions in mammals. Our previous work has shown that kynurenine aminotransferase and alpha-aminoadipate aminotransferase are identical and thus suggests a mechanism by which tryptophan and lysine catabolism may interact in a regulatory fashion. We plan to further purify and characterize the aminotransferase from kidney supernatant and to apply the same methods for purifying the kidney and liver mitochondrial enzymes. We will also try in whole-cell and feeding experiments to evaluate the extent to which the interaction occurs in vivo and whether it has any metabolic significance. We will also attempt in whole-cell and whole-animal experiments to determine whether the several intracellular localizations of the degradative enzymes result in permeability barriers that may influence the degradation rates or pathways. A new method of monitoring the changes in mitochondrial permeability resulting from changes in the Ca ions/Mg ions ratio has been recently developed on this project, utilizing the ability of the mitochondrial kynurenine aminotransferase to respond variably to substrate levels in producing irreversibly a stable product absorbing light at 333 nm. This method will be applied to further studies of regulation of inner membrane permeability. In addition to the specific aims concerning tryptophan and lysine catabolism, we expect the study to reveal new aspects of metabolic regulation in mammals that may be of wider application. BIBLIOGRAPHIC REFERENCES: Tobes, M.C., and Mason, M. (1977) Kynurenine Aminotransferase and alpha-Amino-adipate Aminotransferase: III. Evidence for Activity with 3,5-Diiodo-L-Tyrosine, Biochem. Biophys. Res. Commun., in press. Mason, M., and Tobes, M.C. (1977) Opposing Actions of Ca ions and ATP plus Mg ions in Controlling the Kynurenine Aminotransferase Activity of Isolated Rat Kidney Mitochondria, Biochem. Biophys. Res. Commun., in press.